Method and system for metal drawing and redrawing

ABSTRACT

A system and method of forming a drawn cup for production of a metal container is provided. The system and method contemplates the provision of gap pins to control the relative movements of cup forming features and provide for reduced risk of damage including pinching, chatter, slivering, and thinning of portions of the cup.

This U.S. Non-Provisional Patent Application claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 61/808,111, filed Apr. 3, 2013, the entire disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to methods, systems and devices for drawing and redrawing a metal blank that reduces the occurrence of chatter, hairs, pinching, slivers, and thinning in the formed material. More specifically, the present invention relates to methods, systems and devices for drawing and redrawing metal containers and components thereof, including cups, from a blank of metal stock material that reduce defects in the final product.

BACKGROUND

“Draw and reverse draw” processes for forming a can body are known in the art. In general, a metal sheet is clamped with pins, dies and other similar devices to secure positioning of various features. However, the existing tools and methods frequently create pinching in the metal and the formation of “hairs” or “slivers”. Pinching occurs at circumferential portions of a sidewall during cup formation. Pinching results in undesired anomalies in the formation process, including the hairs and slivers in the formed cup which are unsightly and problematic in the container manufacturing industry.

SUMMARY

Thus, a long-felt and unmet need exists for providing a draw and redraw process whereby pinching of the cup is reduced or eliminated. The present invention provides systems and methods for drawing and redrawing a cup for a metallic container, wherein gap pins are provided for securing and indexing a sheet of stock material, and for controlling or limiting relative positioning of dies and pads.

In operation, a plurality of small blanks, which are designed to receive the guide pins, are initially punched through a metal sheet (typically, an aluminum alloy sheet) as it is indexed. The small blanks surround and/or correspond to the perimeter of a blank that will be deformed in a subsequent draw/redraw process. After forming operations, the sheet is indexed again whereby the blank is located within the cupper tooling. Then, in the next cycle, the following sequence occurs substantially simultaneously: the blank and draw die, which are associated with guide pins, is moved towards the blank and the draw pad such that the ends of the guide pins are received within the small blanks previously punch through the sheet; just before the bottom surface of the blank and draw die contacts the upper surface of the draw pad, the blank and draw die contacts the upper surface of the sheet and forces it against the blanking die cut edge, which sheers the sheet to form a generally circular blank; in conjunction with the movement of the blank and draw die and the draw pad, the die center form punch and upper pressure sleeve are moved towards the also moving draw die; the draw die contacts the bottom surface blank which deforms it in a first direction; the die center form punch contacts the upper surface of the sheet in a second direction to create the finished shape; and the upper pressure sleeve works in conjunction with the upper surface of the draw die to pinch a portion of the blank during final forming of the blank by the die center form punch.

During this process, the guide pins contact an upper surface of the blanking die cut edge just after the blank and draw die create the circular blank. Thus the guide pins prevent contact between the lower surface of the blank and draw die and the draw pad, which allows the material of the blank to be sufficiently constrained during forming operations while allowing the blank material to move laterally with respect to the center axis of the cupping apparatus. This gap provided by the gap pins between the lower surface of the blank and draw die and the upper surface of the draw pad prevents warping of the blank and/or shearing thereof.

In various embodiments, methods of forming a drawn cup having a circular sidewall and an endwall are provided. In one embodiment, a method of forming a drawn and redrawn container body is provided, the method comprising providing a sheet of stock material comprising a plurality of preformed holes for receiving gap pins and positioning said sheet; providing a forming tool, the forming tool comprising: (i) a draw die; (ii) a draw pad; (iii) a blank and draw die; (iv) a center punch; and (v) a plurality of gap pins. The gap pins are provided through said preformed holes, such that said center punch and said draw die are aligned substantially coaxially with a blank to be formed. The gap pins preferably contact the draw pad at certain portions of the method, in contrast with known systems and methods wherein pins do not pass through the sheet of stock material or contact other components of the forming tool. A blank to be formed is provided between the draw pad and the blank and draw die, and a gap between the draw pad and the blank and draw die is approximately equal to a gauge of said sheet. The stock material is sheered into a circular shape by cutting the sheet with a cut edge of the blanking die. The generally circular blank is formed into a first shape by moving the draw die in a first direction and contacting a lower surface of the blank, wherein a portion of the generally circular blank conforms to the draw die under pressure, and wherein the generally circular blank is transitioned out of a space between the draw pad and the blank and draw die. The distal ends of the gap pins then contact a flange portion of said draw pad. Subsequently, an upper surface of the stock material is impacted with the center punch in a second direction to create a second shape, the second shape comprising a cup with a sidewall and an endwall. The tooling components are thereafter separated, allowing the cup to be extracted, and the tooling and sheet indexed or moved relative to each other to enable subsequent forming operations.

The gap pins and methods of use described herein provide a stand off height between tooling components and prevent pinching which is known to cause hairs or slivers in the formed cup.

The Summary of the Invention is neither intended nor should it be construed as being representative of the full extent and scope of the present invention. Moreover, references made herein to “the present invention” or aspects thereof should be understood to mean certain embodiments of the present invention and should not necessarily be construed as limiting all embodiments to a particular description. The present invention is set forth in various levels of detail in the Summary of the Invention as well as in the attached drawings and the Detailed Description of the Invention and no limitation as to the scope of the present invention is intended by either the inclusion or non-inclusion of elements, components, etc. in this Summary of the Invention. Additional aspects of the present invention will become more readily apparent from the Detail Description, particularly when taken together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded cross-sectional view of tooling according to one embodiment of the present invention.

FIG. 2 is a top plan view of a sheet of material according to one embodiment of the present invention.

FIG. 3 is an exploded perspective view of tooling according to one embodiment of the present invention.

FIG. 4A is a perspective view of a gap pin according to one embodiment of the present invention.

FIG. 4B is a cross-sectional elevation view of a gap pin according to one embodiment of the present invention.

FIG. 5 is a flow chart depicting a container forming operation according to one embodiment of the present invention.

FIG. 6A is a cross-sectional elevation view of tooling and a forming step according to one embodiment of the present invention.

FIG. 6B is a cross-sectional elevation view of tooling and a forming step according to one embodiment of the present invention.

FIG. 6C is a cross-sectional elevation view of tooling and a forming step according to one embodiment of the present invention.

FIG. 6D is a cross-sectional elevation view of tooling and a forming step according to one embodiment of the present invention.

FIG. 6E is a cross-sectional elevation view of tooling and a forming step according to one embodiment of the present invention.

DETAILED DESCRIPTION

Referring now to FIG. 1, a drawing apparatus 2 of one embodiment of the present invention is provided. The apparatus 2 comprises an upper pressure sleeve 6, a blank and draw die 8, a blanking die 10 with a cut edge, a draw pad 12, and a draw die 14. The drawing apparatus 2 is provided for forming cups though a draw and reverse draw process while eliminating or reducing the occurrences of hairs, slivers, and similar defects in the resultant cups. In various embodiments, the device 2 is utilized in large stroke double action cupper processes with the novel die set and related tooling. It is contemplated that, in certain embodiments, the drawing apparatus 2 comprises a capacity of approximately 1,000 kN which can produce approximately 15-120 (or more) cups per minute. The device 2 comprises an inner stroke length of approximately 127 mm, an outer stroke length of approximately 203.2 mm and a stroke adjustment of approximately 50 mm, although other stroke lengths could be utilized and benefit from the scope of the invention.

FIG. 2 is a top plan view of a metal sheet 20 from which blanks 22 of the present invention are formed. The metal sheet 20 generally comprises an aluminum alloy sheet. However, methods and devices of the present invention are not limited to the formation of aluminum cups, but may be utilized with any number of suitable materials and alloys as will be recognized by one of skill in the art. A cupper device is cycled and the sheet 20 is indexed to strategically form a plurality of blanks 22 from the sheet 20. Gap pin holes 24 for communication with the cupper device 2 are provided on the sheet 20 proximate to the blanks 22. Methods and devices of the present invention allow for the formation of a plurality of cups from the metal sheet. One such method comprises the steps of providing a metal sheet 20 with a plurality of guide pin-receiving blanks 24. The blank and draw die 8, which comprises associated guide pins 16 is then moved toward the blank and the draw pad 12 such that ends of the guide pins 16 are received within the guide pin-receiving blanks or apertures 24. Subsequently, and prior to the bottom surface of the blank and draw die 8 contacting the upper surface of the draw pad 12, the upper surface of the sheet 20 is contacted with the blank and draw die 8, thus forcing the sheet 20 against the blanking die cut edge 10 and sheering the sheet to form a substantially circular blank 22. In conjunction with the movement of the blank and draw die 8 and the draw pad 12, the die center form punch 4 and upper pressure sleeve 6 are moved towards the draw die 14. The bottom surface of the blank 22 is then contacted with the draw die 14 and the blank 22 is deformed in a first direction. The upper surface of the sheet 20 is then contacted with the die center form punch 4 in a second direction to create the finished shape. During final forming of the cup by the die center form punch 4, a portion of the blank 22 is pinched with the upper pressure sleeve 6 and the upper surface of the draw die 14.

FIG. 3 is an exploded perspective view of a drawing apparatus 2 according to one embodiment. The apparatus 2 comprises a die center form punch 4, an upper pressure sleeve 6, a plurality of guide or gap pins 16, a blank and draw die 8 with a cut edge 10, a draw pad 12 and a draw die 14. The device 2 comprises various features of one particular embodiment of the present invention, and is useful for forming cups from a sheet of aluminum or similar material as shown and described herein.

FIG. 4A is a perspective view of a guide pin 16 according to one embodiment of the present invention. The guide pin 16 generally comprises an elongated shank portion 30 and a head portion 32. FIG. 4B is a cross-sectional view of the guide pin 16 of FIG. 4A. In various embodiments, the shank portion 30 and head portion 32 comprise an overall length of between approximately two inches and ten inches. In certain embodiments, the shank portion 30 and head portion 32 comprise an overall length of between approximately 4.5 inches and approximately 5.5 inches. It will be recognized, however, that these lengths are only exemplary and gap pin size and length may depend on the type of cupper tool, tool design, and design intent of a cup to be formed. Accordingly, no limitation with respect to dimensions is expressed herein.

Referring now to FIG. 4B, a cross-sectional front elevation view of the gap pin 16 is provided. As shown, a transition 31 from the shank portion 30 to the head portion 32 comprises a first transition radius R₁ of between approximately 0.10 inches and approximately 0.025 inches. In a preferred embodiment, first transition radius R₁ comprises a concave radius of approximately 0.06 inches. A second transition radius R₂ is provided, the second transition radius R₂ comprising a convex radius of between approximately 0.10 inches and approximately 0.025 inches. In a preferred embodiment, first transition radius R₂ comprises a radius of approximately 0.06 inches. The transition portion 31 comprises an angled or ramped portion provided between the first and second transition radii, the transition portion provided at an angle of between approximately 30 and 60 degrees with respect to a longitudinal axis of the pin 16. In a preferred embodiment, the transition portion 31 comprises an angle of approximately 45 degrees with respect to a longitudinal axis of the pin 16. A proximal end of the head portion 32 comprises a narrowed diameter D1, wherein D1 comprises a diameter of between approximately 0.450 inches and 0.550 inches. In a preferred embodiment, D1 comprises a diameter of between approximately 0.4995 inches and 0.4998 inches. The transition to the narrowed diameter D₁ comprises a first concave radius R₃ of between approximately 0.010 and 0.020 inches and a second convex radius R₄ of between approximately 0.020 and 0.040 inches. In a preferred embodiment, R₃ comprises a radius of approximately 0.015 inches and R₄ comprises a radius of approximately 0.030 inches.

FIG. 5 is a flowchart depicting a process of creating cups for subsequent forming and processing according to one embodiment of the present invention, wherein gap pins are provided to help control the size and/or shape of a drawn cup. As shown, process step 40 comprises providing a sheet material (e.g. aluminum). A subsequent process step 42 comprises indexing the sheet by a predetermined amount form at least one additional blank from the same sheet. Subsequently, the sheet is further indexed at process step 44 to form smaller blanks from the sheet material, the smaller blanks provided to accommodate gap pins as shown and described herein. A series of steps 45 are provided to form blanks, the series of steps 45 comprising process steps 46-56, wherein the sheet is further indexed 46 to align the smaller blanks with gap pins of a tool. Subsequently, and referring now to step 48, one or more gap pins are passed through corresponding smaller blanks formed in the sheet. Air pressure is provided to the draw pad (12 of FIG. 1) to secure the sheet between the draw pad and the draw die (8 of FIG. 1). In various embodiments, this air pressure comprises a pressure of between approximately 10 and 100 PSI. In preferred embodiments, this air pressure comprises a pressure of approximately 50 PSI. A unique aspect of the present invention lies in that such a pressure is provided for applying a force to the sheet that prevents or minimizes wrinkles or defects during draw operations.

Subsequently, and referring now to process step 50, the gap pins are pushed or biased against the draw pad and create a predetermined off-set or clearance between the draw pad and the draw die. Near the end of the operation, the aluminum area is greatly reduced and ears or peripheral edges become the last points of contact between the draw pad and the blank. The gap pins of the present invention are provided to create an off-set clearance, and the ears are therefore not stressed to the point of failure. Thus, hairs and slivers are reduced or eliminated by the aluminum shearing of the present invention. In various embodiments, it is contemplated that the off-set clearance provided by the gap pins is slightly smaller than the aluminum gauge. For example, the present invention contemplates clearance ranges of between approximately 0.0100 inches and approximately 0.0140 inches.

At process step 52, a reverse redraw operation is provided to complete the formation of the cup. An inner shut height, which comprises a gap distance between the draw pad and the blank and draw die, is controlled via “lift-off” timing. In certain embodiments of the present invention, an inner shut height is approximately 31 inches, with a tolerance of +/−0.050 inches, and an outer shut height is approximately 24.50 inches, with a tolerance of +/−0.060 inches. It will be recognized, however, that these values may vary widely based on various machine and tooling design. In various embodiments, the tooling of the present invention provides a pressure to the metal being formed or shaped throughout substantially the entire forming process. At or near the end of the forming process, pressure in the tooling is relieved by a separation of the components described herein. The lift-off timing of the present invention, which is at least in part a function of the shut heights, prevents clamping of the cup “ears” and thereby prevents hairs, pinching, and slivers associated with prior art devices and methods.

In a preferred embodiment, a gap between the draw pad and the blank and draw die after the reverse redraw step is less than the gauge of the blank, and is dictated by the distal ends of the gap pins which extend a predetermined distance away from the blank and draw die, and preferably extend through the blanking die.

At process step 54 the cup is re-drawn to a final desired shape, preferably by a downward movement of the center form punch. After this formation, the tooling is retracted or released at step 56. Process steps 46-56 may be repeated as desired with a single sheet or the entire process may be repeated by provision of a new sheet.

FIG. 6A is a cross-sectional elevation view of a stage of a cupping operation according to one embodiment of the present invention. As shown, a stock material 20 (e.g. aluminum sheet) is provided in drawing apparatus 2 according to one embodiment of the present invention. A draw die 14 is provided and arranged substantially coaxially with a draw pad 12, a blanking die 10 with cutting edge, a blank and draw die 8, an upper pressure sleeve 6, and a die center form punch 4. Gap pins 16 are provided through blanks or apertures provided in the stock material 20 and through apertures in the blanking die 10. A distal end of the draw pins 16 is provided proximal the draw pad 12, wherein a gap between the pins and the draw pad is less than the gauge of the stock material 20. A substantially circular blank is formed by relative movement of the blanking die 10 and the blank and draw die 8.

FIG. 6B provides a subsequent process step wherein the blank 22 is drawn into a cup at a first cup forming operation. As shown, the draw die 14 is moved upwardly to deform the blank 22 into a partial cup-shaped feature. The aforementioned gap between the gap pins 16 and the draw remains substantially the same as that shown in FIG. 1, such that the gap is less than the gauge of the blank material 22. As shown, the blank material 22 has been formed into a partially cup-shaped feature. At this stage, a gap between the draw pad 12 and the draw die 8 is provided where the blank material 22 previously resided. This gap is equivalent to the gauge of the blank material 22.

FIG. 6C depicts a subsequent process step wherein a cup is fully formed. As shown, the draw die 14 is moved farther upward such that the blank 22 is provided as a cup, and brought to rest against the punch 4 and pressure sleeve 6. As the blank 22 is now formed into a cup, it no longer resides between the draw pad 12 and the draw die 8. Thus, the gap between the draw pad 12 and the draw die 8 is reduced and is less than the gauge of the blank in FIG. 6C. Additionally, the gap pins 16 of FIG. 6C have been brought into contact with the draw pad 12 and no gap between the draw pad 12 and pins 16 remains. At this stage, the gap pins 16 are in force transmitting communication with the draw pad 12.

In certain embodiments, a gap 21 between the draw pad 12 and at least one gap pin 16 is provided in the process steps of FIGS. 6A-6B. The gap 21 at these stages is less than a gauge of the sheet material 22. Subsequent to a drawing operation as shown in FIG. 6B and once the sheet material 22 is translated out from a space between the draw pad 12 and the draw die 8, this gap 21 is reduced or eliminated. Preferably, and referring now to FIGS. 6C-6E, once the blank material 22 is translated out from the space between the draw pad 12 and the draw die 8, at least one gap pin 16 contacts the draw pad 12 and thereby controls the shut height and movement of the draw pad 12 at least with respect to the draw die 8. As shown in FIG. 6C, the gap pin(s) 16 and its contact with the draw pad 12 prevents the draw pad from fully contacting the draw die 8. In certain embodiments a gap remains between the draw pad 12 and draw die 8, this gap being less than a gauge of the material being formed and/or drawn.

FIG. 6D depicts movement of the tooling and an associated redraw step, wherein the blank 22 is impacted by the die center form punch 4. As shown, the punch 4 is moved downwardly and at least partially within a hollow interior of the draw die 14. The punch 4, which comprises a smaller outer diameter than the draw die 14, forms the cup to a desired shape while the gap pins 16 maintain contact with draw pad 12.

FIG. 6E depicts a final cup formation stage, wherein the punch 4 is translated downwardly to form a final cup from the blank 22. As shown, the center form punch 4 is allowed to translate into an interior void of the draw die. Subsequent to the step depicted in FIG. 6E, the tooling may be separated and/or extracted, and the cup removed. Once the cup is removed, the tool is indexed to an another portion of the blank material 22, the gap pins 16 are mated with another set of gap pin holes or apertures 24 corresponding to another portion of the sheet, and the processes of FIGS. 6A-6E is repeated.

In various embodiments, pneumatic compressed air provides a pressure to one or more of the tooling components shown and described herein. For example, an upper tooling component, such as the pressure sleeve 6 may be provided with an “inner” air pressure, which applies a clamp pressure as shown in FIGS. 6C and 6D, and a lower tooling component, such as the draw pad 12, is supplied with an “outer” air pressure, which is shown as a clamp pressure in FIGS. 6A and 6B. In certain embodiments, a force is provided to the pressure sleeve 6 to provide an inner pressure, and a second force is provided to the draw pad 12 to provide an outer pressure. An outer or lower pressure may be utilized in the forming steps of FIGS. 6A-6B, and an inner pressure may be utilized in the forming steps of FIGS. 6C-6D. 

What is claimed is:
 1. A method of forming a drawn metallic cup having a sidewall, and a dome comprising: providing a sheet of stock metal material; forming a plurality of through holes in the sheet, the through holes provided for receiving gap pins of a forming tool; providing a forming tool, the forming tool comprising: i. a draw die; ii. a draw pad; iii. a blank and draw die; iv. a center punch; and v. a plurality of gap pins; providing said gap pins through said through holes such that distal ends of said gap pins are provided proximal a flange portion of said draw pad; wherein the stock material to be formed is provided between said draw pad and said blank and draw die; sheering the sheet to form a generally circular blank; forming the generally circular blank into a first shape by moving the draw die in a first direction, wherein a portion of the generally circular blank conforms to the draw die under pressure, and wherein the generally circular blank is transitioned out of a space between the draw pad and the blank and draw die; contacting said flange portion of said draw pad with the distal ends of the gap pins; contacting an upper surface of the stock material with the center punch travelling in a second direction which is substantially an opposite direction as the first direction to form the blank in a second shape.
 2. The method of claim 1, wherein the forming tool further comprises a blanking die.
 3. The method of claim 2, wherein the blanking die comprises a cutting edge for sheering the sheet.
 4. The method of claim 2, wherein the gap pins extend through apertures in said blanking die.
 5. The method of claim 1, wherein prior to forming the generally circular blank into the first shape, a gap between said draw pad and said blank and draw die is approximately equal to a gauge of said sheet of stock material.
 6. The method of claim 1, wherein after forming the generally circular blank into the first shape, a gap between said draw pad and said blank and draw die is less than a gauge of said sheet of stock material.
 7. The method of claim 1, further comprising indexing said sheet of stock material and performing further drawing and redrawing operations.
 8. A method of forming a drawn and redrawn container body, the method comprising: providing a sheet of stock material comprising a plurality of preformed holes for receiving gap pins and positioning said sheet; providing a forming tool, the forming tool comprising: a draw die; a draw pad; a blank and draw die; a center punch; and a plurality of gap pins; providing said gap pins through said preformed holes, such that said center punch and said draw die are aligned substantially coaxially with a blank to be formed; wherein said blank to be formed is provided between said draw pad and said blank and draw die, and a gap between said draw pad and said blank and draw die is approximately equal to a gauge of said sheet; sheering the sheet to form a generally circular blank; forming the generally circular blank into a first shape by moving the draw die in a first direction, wherein a portion of the generally circular blank conforms to the draw die under pressure, and wherein the first shape is withdrawn from a space between the draw pad and the blank and draw die; wherein an upward movement of the draw pad is limited by the gap pins wherein distal ends of the gap pins contact a flange portion of the draw pad; and contacting an upper surface of the stock material with the center punch in a substantially opposite direction as the first direction to create a second shape comprising a cup.
 9. The method of claim 8, wherein the forming tool further comprises a blanking die.
 10. The method of claim 9, wherein the blanking die comprises a cutting edge for sheering the sheet.
 11. The method of claim 9, wherein the gap pins extend through apertures in said blanking die.
 12. The method of claim 8, wherein prior to forming the generally circular blank into the first shape, a gap between said draw pad and said blank and draw die is approximately equal to a gauge of said sheet of stock material.
 13. The method of claim 8, wherein after forming the generally circular blank into the first shape, a gap between said draw pad and said blank and draw die is less than a gauge of said sheet of stock material.
 14. The method of claim 8, wherein the gap pins prevent said draw pad from contacting said blank and draw die.
 15. The method of claim 8, further comprising indexing said sheet of stock material and performing further drawing and redrawing operations.
 16. A device for forming and reforming a drawn cup for a metal container body, the device comprising: a forming tool comprising a draw die, a draw pad, a blank and draw die, a center punch, a blanking die and a plurality of gap pins; wherein the draw die is provided substantially coaxial with and movable relative to at least one of the draw pad and the blank and draw die; wherein the gap pins comprise a first end, a second end and a predetermined length therebetween; the first ends of the gap pins are secured to the blank and draw die such that the second ends of the gap pins are provided at a fixed distance relative to the blank and draw die; and wherein a shut height between the draw pad and the blank and draw die is limited by said gap pins.
 17. The device of claim 16, further comprising a blanking die, the blanking die comprising a cutting edge adapted for cutting a circular blank of material to be deformed by the device.
 18. The device of claim 16, wherein at least one of the draw pad and the blank and draw die comprise an internal void and wherein the draw die is translatable within said internal void.
 19. The device of claim 16, wherein an outer circumference of the draw die corresponds to an internal diameter of a cup to be formed.
 20. The device of claim 16, wherein the draw die comprises an annular feature adapted to receive the center punch during reforming of a cup. 